Sound recording



April 12 w38 G. R. @Row-:s Zdl v SOUND RECORDING Filed Feb. V1o, 195e INVENTOR. GVEGEGE ,Q Gpo V55 Patented Apr. 12, 1938 PATENT @ENCE SOUNDl RECORDING George R, Groves, Burbank, Calif., assigner to United Research Corporation, Burbank, Calif., a corporation of Delaware Application February 1o, 1936, serial No. 63,079

4 claims.

AThis invention relates toi sound recording' and reproduction, and particularly to the recording of the sound from a'plurality of sources upon y a single record'in such a manner that these vari- 5 ous sounds form aA pleasing tone balance therebetween.

In the production of talkingA motion pictures wherein background sounds, such as music, noise of trailic, etc., are combined with the spoken dia- 1() logue, or other main sources of sound, it is necessary to maintain the proper volume level ratio between the dialogue and the background effects. If'these sound effects are held too loud they mask the dialogue and tend to make it unintelligible,

l5 whereas when they are held too low, in an effort to make the dialogue intelligible, they are no longer life-like and the picture loses its realism. One example of the difficulties encountered in producing the correct volume ratios between the 2G background sound effects and the main sound or dialogue, would be a combining of the effects of a large crowd, such as at a prizeght, with the dialogue comprising the whispering or Inut-v tering of two boxers in the ring during a clinch. Their whisperings, for the purpose of story continuity, must be heard and understoodby the audience, even though hundreds of people in the background are yelling and stamping their feet at the same time.

Usually the average volume level of the background sound would be held sufficiently low to prevent abnormally loud sounds, such as stamp-- ing of the feet, from drowning out or masking the dialogue at these points since this effect would distract the attention of the audience from the main sound or dialogue. However, in this case the lower sounds in the background effects are so low as to be unintelligible, if heard at all'. Heretofore the dialogue and sound effects volume levels were generally controlled by `an operator who manually adjusted the Vmixing panel in an effort to keep the same volume level ratio between the background sound and the dialogue.

By the use of this arrangement it was impossible recording the background effects on a duping record while automatically compressing the volume range thereof during such recording. In the final step of the duping operation the compressed sound effects record is converted into corresponding electrical impulses and these impulses are combined with the uncompressed electrical impulses attained from, and corresponding to, the dialogue sound. The combined sound currents thus produced are fed into. any suitable transducer such as a sound recorder for recording the sound currents uponv a sound record. In copending application Serial No. 63,087 iiled February 10, 1936, a method of and system for producing a similar final result with standard uncompressed sound eiect records is disclosed and claimed.

By compressing the background sound currents the lower amplitude levels are increased in volume, and the higher amplitude levels are generally decreased in volume so as to produce a sound current in which the amplitude levels are maintained at substantially constant amplitude. An arrangement for so compressing the amplitude of the sound current impulses is disclosed and claimed in a co-pending application of Burton F. Miller',Serial No. 42,116, led September 25, 1935.

For further details of this invention, references may be had tothe accompanying drawing whereu Fig. 1 is a schematic view of a sound recording channel for producing a volume compression type of sound record.`

Fig. 2 is a schematic view of aduping channel for dup-ing two or more records upon a single final master record.

Fig. 3 is a circuit diagram of one form of compressor adapted to be employed in the compression recording channel illustrated in Fig. 1.

Referring in detail to Fig. '1, a microphone I0 converts the sound to be recorded intoI corresponding electrical impulses which are passed through an amplifier il and a manually adjustable potentiometer or attenuator l2. plied sound currents are passed through a volume compressor circuit f3, which will be described in detail hereafter, and are then photographically recorded as by means of a light valve it upon a sound record l5. The sound record l5 thus produced will therefore have a record of the sound recorded in microphone lil, but wherein the lower level sound representations are increasedin amplitude to a greater degree than the higher level sound representations.

The am- Fig. 2 shows the circuit for duping the Ycompressed background sound effects and the uncompressed dialogue upon a single final record E9. In this apparatus the compressed sound effects record l5, as produced by the apparatus shown in Fig. l, and an uncompressed dialogue record 2S as produced by any standard sound recording apparatus are placed in translating devices i8 and I9. Each of these translating devices comprises an exciter light 20, and lens and slit combination 2| for focusing a narrow horizontal beam of light upon the lm to be reproduced. The beam of light thus modulated by the sound nlm record is allowed to fall upon a suitable photo-electric cell 23 or 29.Y The speech currents produced in the photo-electric cell 23 are passed through an amplifier 25, a potentiometer 2B and thence into a channel bus 2l. The speech currents corresponding to the uncompressed dialogue sound lm record 28 as generated in a photo-electric cell 29 arepassed through an amplifier 30, a potentiometer-3| and are combined at 21 with the background sound currents from the lm I5. The combined sound currents thus produced are passed through one or more suitablechannel amplifiers 32, a channel potentiometer 33, and then into a suitable sound recorder for the lm I6, such as a light valve 34. Preferably Vat this point the speech currents are passed through a noise reduction circuit 35 of the standard shuttering or biasing type in order to produce a variable area or variable density noise reduction sound track. However, the volume compression-expansion typeV of sound recording may be employed here by introducing a volume compressor circuitV in the channel in place of the noise reduction circuit 35.V In this case the duped record kI6 would be of the compressed type and may be reproduced in sound reproducer employing a volume eX- pansion circuit such as disclosed and claimed in the co-pending application of Burton F. Miller, above identified.

Referring to Fig. 3, which is a circuit diagram of a compressor circuit adapted to be employed in the recording channel of Fig. 1, the input 3l is coupled through an input transformer 3B to the gird-cathode circuit of a pair of im-V pedance tubes 39 and 40. Tubes 39 and 40 are placed in series in a circuit between the input transformer 33 and an output transformer 4|. A pair of leads 42 is shunted across the output of transformer 4| to feed aV portion of the sound currents passing there-through, serially, through an amplier 43, a rectifierV 44 and a filter 45. The output terminals of filter 45 are connected in series in a common lead of the grid-cathode circuits of tubes 39 and 40. A static negative potential is applied to the grids of tubes Y39 and lili through the drop in potential across the re-` sistance VLl'provided in series with a direct current power supply, generally indicated at 48. It will thus be seen that a varying grid bias is provided by the rectified speech currents obtained through the Vpair of leads 42, which changes in accordance with the amplitude of the currents passing through the compressor circuit. The polarity of the output terminals of lter 45 is so arranged that at higher amplitude levels the negative grid bias is increased, thus increasing the impedance of tubes 39 and 40, thus decreasing the final output levels of these higher amplitudes.

In order to prevent the impedance of tubes 39 and 40 from becoming too high a resistance 50 of about 100,000 ohms, and acondenser 5| in series is shunted across the cathode-anode circuit of tube 39. A similar resistance 5?. and condenser 53 in combination is shunted across the cathode-anode circuit of tube 40. In order to prevent the impedance of tubes 39 and 40 from dropping to an extremely low value a resistance 54 of about 100,0007ohms isrprovided in series in the ugrid-cathode circuits of tubes 39 and 40. By the use of resistance 54 any tendency for the grids of tubes 39 and V4|) to be driven positive by high 'signal levels will be counteracted by the drop in potential across this resistance 54 due to the grid current flow.

Although the above description and accompanying drawing have described and illustrated "the invention'in conjunction With the sound-onlm type of sound record, it is to be understood that any type of sound record may be employed such as wax, Wire, etc., without departing from the scope of the invention. Y

Having thusdescribedthe invention, what is Vclaimed as new and desired to be secured by Letters Patent is:

1. The method of producing a standard noise reduction record of a primary sound and of a secondary sound'comprising translating the primary sound into a sound record having variations in amplitude directly proportional to the variations in amplitude of said source, translating said secondary Vvsound into a sound record in which the amplitudes have been varied in accordance with a predetermined ratio, simultaneously translating said records into sound currents varying in accordance with the records, combining said currents into a common duping channel while varying the relative amplitudes therebetween sothat higher level amplitudes of said secondary Vsound do not interfere with said primary sound amplitudes, lwhile maintaining said low level sounds at an amplitude to maintain a high sound to noise ratio, and recording said currents into a standard noise reduction record.Y

2. lThe method of producing a sound print having background sound effects and dialogue therein comprising translating said dialogue sounds -into aysound'record in which the amplitudes of said record are proportional to the'amplitudes of said dialogueY sounds, translating the back' ground soundjeifects into a record thereof in Whichrthe amplitudes are not proportional to the original amplitudesbut vary in a predetermined ratio, simultaneously translating each of said records into corresponding electrical currents, combiningV saidelectrical currents in a common duping channel, and adjustingthe amplitude levels of each of said currents before their cornbination, said adjustment being such that the higher'amplitudes Vof said sound effects do not interfere with said dialogue sounds, and recording said combined currents into a standard noise reduction Y record.

3. The Vmethod'of producing a sound print in accordance with claim 2, in which the translation of said background effects into a recordcomprises reducing the higher level amplitudes to a larger extent than the lower level amplitudes.

4. The art of producing a combination sound print ofY dialogue sounds occurring at different times than background sounds to be combined therewith comprising recording said dialogue sounds in a normal Vmanner to maintain the same Variation in amplitude on the record as the variation in amplitude of the original dialogue, recording the sound effects while compressing said sound eiects to vary the larger amplitudes to a.

greater degree than the smaller amplitudes, si-

multaneously translating both of said records into electrical currents and combining said cur- 

